I have an amd64 based PC and I wanted to set up an ARM based Ubuntu 22.04 so that I can implement ARM64/aarch64 support in Arcemu, a pet project of mine.
For this obviously one needs

• A virtual machine / emulator that can run aarch64 code on the amd64 platform
• An OS image to boot

I found a short guide that was supposed to help me with this on Ubuntu’s wiki.

It basically describes how you can use QEMU system emulator to emulate an ARM64 system and boot an Ubuntu cloud image with it.

Unfortunately it wasn’t enough because

• It required root, but I wanted it to run as a simple unprivileged user
• I couldn’t log in after boot

So I started digging, and as it turned out I you have to seed cloudinit with parameters when first booting to create a new user, and also had to pass some different parameters to QEMU.

This post will describe all the steps required to make this work.

Download dependencies

Install QEMU for Arm emulation, and cloud image utils:

apt-get install qemu-system-arm qemu-efi cloud-image-utils

Grab Ubuntu 22.04 for ARM cloud image:

wget http://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-arm64.img

Copy the ARM UEFI for the virtual machine:

cp -v /usr/share/qemu-efi-aarch64/QEMU_EFI.fd .

Prepare the cloud image

Resize the image so we have some more free space after boot:

qemu-img resize jammy-server-cloudimg-arm64.img +20G

Prepare for first boot

Now we need to create the data for cloudinit so it creates a new user when first booting.

First we create a password, with the mkpasswd command. It will ask you to type a password and print the encrypted version of it that will have to be passed to cloud-init.

mkpasswd --method=SHA-512 --rounds=4096

Create the configuration file for cloud-init: Create a text file cloud.yml with the following contents:

users:
  - name: USER
    lock_passwd: false
    passwd: Password generated by mkpasswd
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: sudo
    shell: /bin/bash
	

Obviously where it says “Password generated by mkpasswd” you should paste the password created in the previous step.

This instructs cloud-init to

• Create a new user with the name USER. You can use whatever username you’d like
• Unlock password login for the user (Important, because by default this is locked!)
• Sets the generated password
• Allows sudo without entering the password
• Sets the shell to be bash

Having done so we create a virtual disk from this yaml:

cloud-localds --disk-format qcow2 cloud.img cloud.yml

The output file cloud.img is a virtual disk that needs to be mounted into the virtual machine.

Boot the virtual environment

Now we’re ready to boot the virtual / emulated ARM system:

qemu-system-aarch64 \
-m 4096 \
-smp 5 -cpu cortex-a57 -M virt \
-nographic \
-bios QEMU_EFI.fd \
-device virtio-net-device,netdev=eth0 -netdev user,id=eth0,hostfwd=tcp::2222-:22 \
-drive if=none,file=jammy-server-cloudimg-arm64.img,id=hd0 -device virtio-blk-device,drive=hd0 \
-drive if=none,id=cloud,file=cloud.img -device virtio-blk-device,drive=cloud

A little explanation for the parameters here:

• -m 4096 Allocates 4096 MB of RAM to the virtual machine.
• -smp 5 Allocates 5 virtual CPUs to the virtual machine.
• -cpu cortex-a57 Emulate a cortex-a57 CPU
• -M virt Use the “generic virtual platform” that is we’re not emulating any particular real hardware. This is commonly used for VMs
• -nographic We don’t need the QEMU GUI
• -bios QEMU_EFI.fd The UEFI BIOS file
• -device virtio-net-device,netdev=eth0 -netdev user,id=eth0,hostfwd=tcp::2222-:22 We use a usermode emulated network device and forward the virtual machine’s port 22 to the host’s port 22 (so we can SSH)
• -drive if=none,file=jammy-server-cloudimg-arm64.img,id=hd0 -device virtio-blk-device,drive=hd0 This is just the cloud image that we downloaded and prepared.
• -drive if=none,id=cloud,file=cloud.img -device virtio-blk-device,drive=cloud This is the cloud-init virtual disk which only needs to be attached on first boot.

After first boot

You can log in to the virtual machine with the generated user / password and do whatever you wish.

If you want to use SSH as well you need to set up the SSH keys or enable password login. Then you can just ssh via the forwarded port:

ssh -p 2222 USER@localhost

Where USER is the username you typed into the cloud.yaml file earlier.